[keyframe] Specify the input's colorspace when it is sRGB

JPG images are always supposed to be in sRGB. When this information is
available, it is better to include it in the "fromColorSpace" when writing
the output to ensure the colorspace is appropriate.

src/aliceVision/keyframe/KeyframeSelector.cpp

@@ -454,6 +454,7 @@ bool KeyframeSelector::writeSelection(const std::vector<std::string>& brands,
             inputSpec.extra_attribs = image::readImageMetadata(currentImgName);
             int orientation = inputSpec.get_int_attribute("Orientation", 1);
             float pixelAspectRatio = inputSpec.get_float_attribute("PixelAspectRatio", 1.0f);
+            std::string colorspace = inputSpec.get_string_attribute("oiio:Colorspace", "");
 
             oiio::ParamValueList metadata;
             metadata.push_back(oiio::ParamValue("Make", brands[id]));
@@ -479,6 +480,9 @@ bool KeyframeSelector::writeSelection(const std::vector<std::string>& brands,
                 options.fromColorSpace(image::EImageColorSpace::SRGB);
                 options.toColorSpace(image::EImageColorSpace::AUTO);
             } else {  // Otherwise, the frames have been read without any conversion, they should be written as such
+                if (colorspace == "sRGB")
+                        options.fromColorSpace(image::EImageColorSpace::SRGB);
+
                 if (outputExtension == "exr")
                     options.toColorSpace(image::EImageColorSpace::NO_CONVERSION);
                 else